1. Field of the Invention
The invention relates generally to electrical terminals and, more particularly, to electrical terminals providing for electrical engagement of wire conductors.
2. Background Art
Historically, various types of assemblies have been developed for electrically and conductively interconnecting devices to be electrically energized to sources of electrical power. For example, it is well known to provide various spatial areas of residential, commercial and industrial establishments with electrical receptacle units permanently (through fuses, circuit breakers or other emergency shut-off elements) and conductively connected to one or more sources of main utility power. Each of the receptacle units typically comprises one or more engaging assemblies often referred to by the term “female receptacle.”
These receptacle units are conventionally mounted in stationary walls or, alternatively, in the case of modern and modular office furniture systems, in moveable wall panels or even within work surfaces. Devices to be electrically energized often comprise receptacle plugs having two or more prongs or blade terminals adapted to be conductively engaged within the female receptacles. The prongs or blade terminals are conventionally referred to by the terms “male” plugs, prongs, blades or terminals. The receptacle plugs are typically interconnected to the circuitry of the device so as to be energized by wires extending through flexible insulative cords or the like. This type of male/female electrical interconnection configuration to provide removable or releasable conductive engagement is utilized in a myriad of electrical connector arrangements. For example, in addition to electrical energization of relatively large and discrete devices (such as lamps, televisions, stereos, typewriters, etc.), male/female interconnection configurations are also utilized internally in electrical devices such as computers and associated peripherals. In addition, male/female electrical interconnection arrangements are also utilized in a number of other applications, such as internal circuit wiring for electrical apparatus of modular office systems and the like.
In the design of male/female electrical interconnection configurations, it is of primary importance to provide a secure and stationary electrical contact between the conductive surfaces of the elements of the electrical receptacle and the conductive surfaces of the prongs or blade terminals. It is also of primary importance to provide surface connections having relatively little resistance. In view of the foregoing, various types of interfaces have been developed for engaging male prongs or blade terminals with mating female receptacles. For example, it is known to utilize an opposing pair of cantilever beams within the female receptacle, which provide a single point of contact on each side of an inserted male terminal. Other known arrangements include the use of single cantilever spring pressure, backed with a steel or similar spring supported within a plastic housing. This type of arrangement will conventionally provide a single point of contact at the electrical interface.
It has become known that it is preferable to provide as many interface points of contact as is reasonably possible, while still maintaining a releasable engagement. For example, an arrangement for providing four contact points is disclosed in Sasaki et al, U.S. Pat. No. 4,795,379 issued Jan. 3, 1989. The Sasaki et al patent refers to the concept that it has been known to utilize certain types of electrical connections in computers, telecommunications equipment and other data processing equipment, which are in the form of a receptacle contact having four resilient cantilever contact members extending forwardly from a base. The contact members are adapted to provide an electrical connection with a tab contact inserted from the front of the receptacle unit. The tab contact is electrically engaged by four leaves from four directions. The four leaves can be arranged as opposing pairs, with each pair arranged orthogonally.
In this type of arrangement, electrical engagement is made with the tab contact at four points, thereby increasing reliability of the receptacle contact relative to a contact arrangement having only two contact points. Sasaki et al also explains that a problem can arise in that a possibility of an incomplete electrical engagement can be caused by foreign matter on the surface of the tab contact. In addition, one of the pairs of contact members may engage the edge surfaces of the tab contact. The edge surfaces of the tab contact are typically the surface edges formed when the contact is made by stamping a sheet of conductive material. The surfaces are often rough in comparison with the planar rolled or formed surface of the sheet, and thus have a lower contact reliability. Accordingly, these contact members may not provide a reliable electrical connection, and a greater insertion force may be required at the time of insertion.
As an improvement, Sasaki et al describes a receptacle contact having opposed leaf spring members formed by two parallel plates linked through a U-shaped portion extending between adjacent sides of the leaf spring members. The leaf spring members include first spring arms and second spring arms formed integrally with the spring members.
The first spring arms and second spring arms are opposed to each other, and outer contact and inner contact members are formed at the free ends of the spring arms, which are also opposed to each other. Additional contact members are located to the rear of the first set of contact members. The spring arms extend side by side from the leaf spring members, with the outer contact members being slightly twice the width of the inner contact members. The contact members are arcuate to facilitate insertion of a tab contact there between.
The receptacle contact described in Sasaki et al is formed by stamping from a suitable metal sheet having the desirable conductive and spring characteristics. The stamping process is performed by shaping the metal sheet in an appropriate configuration, and then folding the spring arms to the shape required, while folding another portion into a U-shape. In use, the tip of a tab contact can be inserted into the space between the outer contact members opposed to each other at the front portion of the receptacle contact. Upon insertion, upper and lower surfaces of the contact are brought into a wiping engagement with the outer contact members. Accordingly, foreign matter on upper and lower surfaces of the contact is removed. When the contact is inserted further, the upper and lower surfaces which have been cleaned by the outer contact members are also wipingly engaged by the inner contact members. In this manner, a relatively greater electrical connection reliability between the tab contact and the inner contact members is provided. In addition, the outer contact members and inner contact members are in electrical engagement with upper and lower planar surfaces of the tab contact, and not with side surfaces which may comprise the cut edge surfaces of the contact. Accordingly, this decreases the force needed to insert the contact into the receptacle contact, thereby improving reliability of electrical connection.
In addition, the length of the spring arms, which provide the contact force created between the outer contact members and the tab contact, is longer than the length of the spring arms which provide the contact force between inner contact members and the tab contact. Accordingly, the insertion force is reduced by reducing the contact force created between the tab contact and the outer contact members, which clean the upper and lower surfaces of the tab contact. In this manner, the initial insertion force of the tab contact within the outer contact members is less than the insertion force of the inner contact members.
The foregoing background description primarily discusses issues associated with electrical terminals having means for conductively engaging components such as male blade terminals, prongs and the like. One difficulty which arises with respect to the electrical industry relates to situations where it is desirable to provide for electrical engagement along a solid wire or similar component. In the past, such interconnections have been made at the ends of solid wires, which may not provide for terminal connections in appropriate locations. Otherwise, to provide for electrical engagement at a location intermediate the ends of a solid wire, it has been known to utilize splicing or other means which require a “cutting off” of solid wire continuity, so as to engage with a terminal. Such activities can lessen the quality and integrity of electrical conductivity through the solid wire, particularly at connection junctions between cut solid wire and terminal elements. Also, such splicing or similar activities, along with the requirement to provide electrical terminals having a substantial metallic content, can add substantial expense with respect to labor for assembly and material content. Accordingly, it would be advantageous to provide for conductive electrical terminal contact at intermediate locations along a solid wire, without requiring continuity of the wire being disrupted.